Field of the Invention
The present invention relates to a dental treating apparatus with a hand piece, and more specifically to a dental treating apparatus that causes a cutting tool for cutting and enlarging an inner wall of a root canal of a tooth to be driven.
Description of the Background Art
In dental treatment, a root canal of a tooth is cut and enlarged for treatment in some cases. For this treatment, a dental treating apparatus having a cutting tool (referred to as “file or reamer”) attached to a head unit of a hand piece is used and the cutting tool is driven to cut and enlarge the root canal of the tooth. Japanese Patent No. 3264607, Japanese Patent No. 3615209 and Japanese Patent No. 3676753 disclose various types of driving control in order to, for example, prevent breakage due to a load applied to the cutting tool when the dental treating apparatus causes the cutting tool to be driven to cut and enlarge the root canal of the tooth.
A dental treating apparatus disclosed in Japanese Patent No. 3264607 includes detecting means for detecting a load applied to a cutting tool, and control means for reversely rotating a cutting tool driving motor when the detected load reaches a preset reference.
A dental treating apparatus disclosed in Japanese Patent No. 3615209 includes driving means for driving a cutting tool, load detecting means for detecting a load applied to the cutting tool, root canal length measuring means for measuring a root canal length by using the cutting tool, reference load setting means for arbitrarily presetting a reference load, and control means for controlling the driving means. When the load detected by the load detecting means exceeds the reference load, the control means controls the driving means by any one of the operations of stopping driving of the cutting tool, reducing an amount of driving, reversing rotation, and repeating normal rotation and reverse rotation, such that the load applied to the cutting tool is reduced. Furthermore, based on a value of the root canal length measured by the root canal length measuring means, the control means controls the driving means such that the amount of driving the cutting tool becomes smaller as a distance from the cutting tool to a root apex becomes shorter.
A dental treating apparatus disclosed in Japanese Patent No. 3676753 includes driving means for driving a cutting tool, root canal length measuring means for measuring a root canal length, and control means for controlling the driving means such that the driving force of the cutting tool changes in accordance with a value of the root canal length measured by the root canal length measuring means. The control means includes number-of-rotations control means for controlling the number of rotations of the cutting tool. Based on the value of the root canal length measured by the root canal length measuring means, the number-of-rotations control means controls the driving means such that the number of rotations of the cutting tool becomes smaller as a distance from the cutting tool to a root apex becomes shorter.
In a dental treating apparatus disclosed in Japanese National Patent Publication. No. 2003-504113, a cutting tool is rotated clockwise or counterclockwise by a desired first rotation angle, and then, is rotated by a second rotation angle in a direction opposite to the first rotation angle. In order to discharge a cut piece from a root canal, the cutting tool is driven such that the first rotation angle is larger than the second rotation angle.
The cutting tool for cutting and enlarging the root canal of the tooth cuts into the root canal wall and contributes to cutting of the tooth when rotated clockwise, for example, whereas the cutting tool does not cut into the root canal wall and does not contribute to cutting of the tooth when rotated counterclockwise. For example, in the dental treating apparatus disclosed in Japanese National Patent Publication No. 2003-504113, twist driving is performed in which driving for rotating the cutting tool clockwise by a desired first rotation angle and then rotating the cutting tool counterclockwise by a second rotation angle is repeated. Therefore, when the cutting tool is rotated clockwise, the cutting tool cuts into the root canal wall and the load is applied to the cutting tool. On the other hand, when the cutting tool is rotated counterclockwise, cutting into the root canal wall is lessened and the applied load is also reduced.
However, if cutting into the root canal wall is not sufficiently lessened and the applied load is not sufficiently reduced when the cutting tool is rotated counterclockwise, the cutting tool further cuts into the root canal wall and more load is applied to the cutting tool when the cutting tool is rotated clockwise again, as compared with when the cutting tool is first rotated clockwise. Namely, in the dental treating apparatus disclosed in Japanese National Patent Publication No. 2003-504113, if the load applied to the cutting tool is not sufficiently reduced when the cutting tool is rotated counterclockwise, the excessive load is applied to the cutting tool when the cutting tool is rotated clockwise again, which resulted in breakage of the cutting tool.
In addition, in the dental treating apparatus disclosed in Japanese National Patent Publication No. 2003-504113, the cutting tool is rotated clockwise or counterclockwise by the desired first rotation angle, and then, is rotated by the second rotation angle in the direction opposite to the first rotation angle, and thus, the rotation that does not contribute to cutting of the tooth is inevitably included, which resulted in a decrease in tooth cutting efficiency.